Wednesday, August 3, 2011

Alveolar soft‐part sarcoma is a rare tumor of unknown origin that tends to affect children and young adults. The tumor has a relatively indolent clinical course, with survival rates of about 75% at 2 years. The ultimate prognosis, however, is poor due to late metastases, with survival dropping to 15% at 20 years. The prognosis, however, seems to be considerably better in children.

Histologically, these tumors are characterized by uniform nests of polygonal tumor cells that are separated by fibrovascular septa and delicate vascular channels. The cells inside the nests are discohesive, which together with the fibrovascular septa, resemble the pattern of alveoli in the lung.

Intravascular tumor extension is seen on histology in most cases.

Alveolar soft‐part sarcoma typically presents in the lower extremities of young women. It also has a predilection for children, in which case the gender ratio appears more equal between males and females. In addition, a substantial percentage of these tumors occurs in the head and neck in children, often occurring in the orbit or tongue. Tumors occurring in these locations tend to have a better prognosis, possibly due to their small size at the time of diagnosis.

Imaging findings are nonspecific. However, features such as myxoid or cystic change and hemorrhage are unusual at histology.

The figure above shows an alveolar soft part sarcoma in the right calf of a young woman. The mass extends along the lateral and posterior compartments of the calf and has engulfed and destroyed the fibula. The tumor is predominantly hypointense on T1-weighted images and hyperintense on T2-weighted images. There is mild, heterogeneous enhancement with central areas of necrosis.